The many unique and functional properties of glass make it a most useful material, particularly for laboratory and industrial glassware and apparatus. This is especially true of the borosilicate glasses which are hard and resistant to corrosion by most chemicals. Such glasses along with quartz and high silica glasses also have low expansion coefficients and are therefore more resistant to thermal shock failures than soda lime, or other glasses with higher expansions. Borosilicate glass, like most other glass,* is highly brittle and sensitive to mechanical shock or impact. This is further magnified by the presence of the many little flaws generally present in all commercial glassware. Such flaws act as stress raisers which greatly increase the impact sensitivity and failure probability of the material. It is apparent that the brittle failure of glass makes it a hazardous material for containing chemicals and the like. Failure is frequently catastrophic, that is a light impact may not just crack a glass vessel, but actually cause it to break with the release of its contents. Laboratory accidents frequently are the results of broken glass, and glass shattering impacts, explosions and implosions. Industrial pip lines, for example, used for hot and corrosive fluids are prone to catastrophic failure by impact. FNT * Certain chemically treated glasses are considerably more shock resistant but nevertheless are subject to brittle failure. This is also true of glass-ceramics.
One approach to the protection of glass pipe is in the use of plastic jackets or wound tape coatings, i.e., polyesterglass fiber. This type of protection is used primarily for pipe transporting fluids, since the use of plastic does not allow the heating of glass beyond the relatively low temperature limitations of the polymeric coating. Therefore, it cannot be used for many types of glassware, both industrial and laboratory, where heating is required. The tape wrap adds nothing to the strength or intrinsic pressure capability of the glass pipe.
The literature describes metal coated glass objects such as light reflectors; flat plates for electronic circuits, and the like. We have not found reference to metal coated glassware particularly for use as laboratory ware, chemical processing applications, etc.
In all the literature examined we have noted the emphasis on glass surface preparation in order to obtain good adherence or bonding between the glass surface and metal coating. This need for good bonding is a theme common to all the literature we have seen. Several references indicate the need to leach, etch, or otherwise treat the glass surface in order to obtain the best possible adherence. This adherence requirement is in direct contradistinction to our coating technique which requires the use of anti-bonding films to consistently obtain detect-free, strengthened, glassware. This will be made clear in the following description of the invention.
What has been said hereinbefore about the shortcomings in the prior art with respect to a need for providing to glass items adequate impact resistance, improved heat distribution, adequate resistance to breakage at higher pressures, and fail-safe protection can also be said of molded graphitic items such as, for example, molded graphite and impervious (polymeric resin infiltrated) graphite tubes or pipes for heat exchangers and the like. Some of the shortcomings of conventional impervious graphite heat exchange tubes are described by Dennis G. Hills in an article in the Dec. 23, 1974 issue of Chemical Engineering, at page 83:
The limitations on this design are the pressure limits, which are relatively low. The highest recommended operating temperature is approximately 180.degree. C and the operating pressure 75 psig with liquds and up to 50 psig with steam.
Heat exchange tubes made of graphite which are to be subjected to elevated pressures are made conventionally with very thick walls. Thus, for heat exchange equipment in which there is pressure inside the graphite tubes, conventional treatment requires a sacrifice of heat transfer capability due to the requisite thick tube walls. The present invention makes such sacrifice in heat transfer capability unnecessary, even though the basically graphite tubes are to be used under pressure. Also, the present invention makes it possible to use graphite tubes in equipment which involves substantially higher pressures than was heretofore believed possible without sacrificing any heat transfer capability. Using the present invention, the walls of the graphite tubes can actually be made thinner than those used in conventional graphite tube heat exchange practice, so long as the graphite remains thick enough and retains enough surface and porosity integrity to accomplish the desired degree of corrosion prevention. Graphite pipe walls could be reduced in thickness by half or more if the pipe were nickel armored, for example, in accordance with this invention. Although graphite (including impervious graphite) has a higher conductivity than nickel (975vs550), the decreased wall thickness of the pipes made possible by this invention would more than compensate, in view of the relatively thin metal coatings that are used, so that the combined thermal conductance of the thinner walled metal-coated graphite tubes or pipes would be higher than that of conventional graphite pipes. Even without changing the thickness of the carbon (or graphite) tube walls, the thin metal armor would detract very little from the thermal conductance property of the uncoated tubes.
The present invention seeks to overcome certain of the basic disadvantages of brittle objects such as glassware by providing a strong, metallic, safety armor over the outer surface of such objects. Also it seeks to improve the heat distribution, pressure capability and other properties of glassware and other brittle engineering materials, made for example, of quartz, graphite, glass-ceramics, carbon, graphite, cermets, semi-conductor materials, and the like.